Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests

[Christoph Hellwig]

On Thu, Aug 30, 2018 at 01:11:18PM -0600, Jens Axboe wrote:
> I think this belongs in the caller - both the validity check, and
> passing in NOMERGE for this type of request. I don't want to impose
> this overhead on everything, for a pretty niche case.

It is just a single branch, which will be predicted as not taken
for non-P2P users.  The benefit is that we get proper error checking
by doing it in the block code.